1. Field of the Invention
The present invention relates to a disc brake device for a vehicle such as a motorcycle. More specifically, the present invention relates to a disc brake device for a vehicle which improves the heat radiation characteristics of a disc rotor.
2. Description of the Related Art
Several methods have been developed to improve heat radiation of a disc rotor. For example, an outer diameter of a wheel hub mounting part can be made larger than a mounting pitch circle of the disc rotor to contact the side surface on the inner circumference side of the disc rotor on the mounting part continuously in the circumference direction, thereby increasing a contact area. An example of such a method is disclosed in Japanese Published Unexamined Utility-Model Application No. Sho 63-106925 (FIGS. 3 and 4).
Another method includes forming radial air vent grooves in the jointing part of a wheel hub and a disc rotor to improve heat radiation. An example of such a method is disclosed in Japanese Published Unexamined Utility-Model Application No. Hei 2-110727 (FIGS. 1 to 9).
Yet another method includes forming thinning holes in the middle part between the contact part of a disc rotor with a wheel hub on its inner circumference side and a caliper sliding contact part on its outer circumference side to reduce the weight of the entire disc brake device. An example of such a method is disclosed in Japanese Published Unexamined Patent Application No. Hei 8-14287 (FIGS. 4 and 6).
However, in a disc brake device, improvement in heat radiation of a disc rotor and reduction of the weight of the entire disc brake as an unsprung weight are required at the same time. Therefore, each of these methods has disadvantages.
For the improvement in heat radiation of a disc rotor, effectively, the outer circumference part of the side surface of a wheel hub and the side surface of the inner circumference part of a disc rotor are contacted continuously in the circumference direction to increase a contact area. The contact area is enlarged up to a caliper sliding contact part, which is limited for itself.
Since the diameter of the wheel hub is made larger to provide for a mounting part, the contact part of the disc rotor must be thinner to achieve weight reduction. The amount of thinning is limited, however, since necessary stiffness is required.
Further, in the case of a motorcycle, consideration must be given to facilitating the passing-through of crosswind. This is particularly important at the front wheel.
Accordingly, an object of the present invention is to realize these requirements.